identity_map.rb

require "moneta"
require 'moneta/redis'

module DataMapper

  # Tracks objects to help ensure that each object gets loaded only once.
  # See: http://www.martinfowler.com/eaaCatalog/identityMap.html
  class IdentityMap < Moneta::Redis
    extend Deprecate

    deprecate :get, :[]
    deprecate :set, :[]=
    
    def [](key)
      resource = Marshal.load(super(key))
      resource.unmarshal
    end
    
    def []=(key, resource)
      super(key, resource.marshal)
    end
    
  end # class IdentityMap
end # module DataMapper

resource.rb

    def marshal
      @repository = nil
      marshalled_resource = Marshal.dump(self)
      @repository = model.repository
      marshalled_resource
    end
    
    def unmarshal
      @repository = model.repository
      self
    end